In forming liners in closures, it has been common to compression mold the liner. Typical patents showing such a method and apparatus are U.S. Pat. Nos. 2,072,536, 2,930,081, 3,827,843, 4,274,822, 4,312,824 and 4,497,765.
One of the problems in compression molding of liners is that of controlling the molding force when molding liners directly into a closure such that sufficient molding force is used to fill the required seal volume and not produce shorts and, at the same time, to limit this same force to avoid flashing of the liner. This force should be consistent and equal on each of all toolings to avoid process variability. The use of compression springs to control this force would not be consistent from tool to tool due to the variability of the rating of the springs and due to the inevitable fatigue that would be induced after substantial length of running. Further, means to readily adjust the molding force of all toolings with one adjustment of system pressure is desirable.
Among the objectives of the present invention are to provide a method and apparatus for compression molding liners in plastic closures wherein the molding pressure on the charge that is being shaped to define the liner is accurately controlled; wherein when an array of tooling is provided, each set of tooling functions independently of the other; wherein the forming pressure can be readily changed; and wherein the tooling can be readily assembled and removed.
In accordance with the invention, the method and apparatus for compression molding closure liners includes providing a first assembly and second assembly which are movable toward and away from one another. The first assembly of tooling includes a liner forming member, a closure engaging sleeve thereon, and the second assembly has a closure supporting pad thereon. A cam is associated with the first assembly of tooling for moving the closure engaging sleeve into engagement with a closure and the liner forming member into position for compression molding a charge of plastic extrudate in the closure when it is supported on the closure supporting pad. A gas cylinder is associated with the closure supporting pad containing gas at a predetermined pressure providing a controlled molding pressure on the plastic. In a preferred mode, a plurality of sets of tooling are provided in circumferentially spaced relation to one another. Means are provided for readily changing the pressure.